Matrix displays are commonly used for a wide variety of applications including portable computer displays, displays for various instruments, and camcorder viewfinders, to name a few. The most commonly used matrix display is currently the liquid crystal display ("LCD"). In liquid crystal displays and other matrix displays, individual pixels are individually illuminated at locations where an energized row overlaps an energized column. A desired image is created by sequentially controlling the illumination of each pixel in a row, and then similarly scanning each row in sequence.
The pixels of liquid crystal displays are illuminated substantially uniformly across the surface of the pixel. The pixels are generally separated from each other by a dark border or mask in order to improve the contrast of the display. However, abrupt changes in illumination of adjacent pixels, such as at the borders of letters, can produce an uneven appearance, i.e., a jagged edge or border. Also, gray scale images displayed on liquid crystal displays can have a grainy appearance. Attempts have been made to solve these problems by placing a depixellation film on the outer surface of liquid crystal displays to "blend" light emanating from adjacent pixels, thereby eliminating jagged edges and graininess. Such depixellation film is basically composed of a large number of microlenses, generally of the graded refractive index type, mounted on a transparent substrate or film. Such depixellation films are available from a variety of manufacturers, including Microsharp US, of Nashua, N.H. These conventional depixellation films have significantly improved the viewing characteristics of liquid crystal displays.
Another variety of matrix display is the field-emission display in which electrons are emitted from cold-cathode emitters mounted on a baseplate faceplate, similar in composition to the faceplates of cathode-ray tubes, attracts the emitted electrons to create an image variable through the faceplate. The sizes of the pixels used in field-emission displays can be made very small. For this reason, as well as for other reasons, the jagged edges and graininess often occurring in liquid crystal displays is not as significant a problem in field-emission displays. Thus, the depixellation film is not as apparent for field-emission displays. However, unlike the uniform illumination of liquid crystal displays, the pixels of field-emission displays are generally non-uniformly illuminated. The difference in the pixel illumination characteristics between liquid crystal displays and field-emission displays are best explained with reference to FIGS. 1-3. FIG. 1 illustrates a conventional matrix display 10 which may be either a liquid crystal display or a field-emission display. FIG. 2 is a graph 20 of the illumination characteristics of a liquid crystal display taken along the line 2--2 of FIG. 1. (Only seven of the hundreds or thousands of pixels along the line 2--2 are shown.) As illustrated in FIG. 2, pixels 22-28 and 34 are illuminated to substantially the same, relatively high intensity, while pixels 30 and 32 are substantially dark. A border 38 between each of the pixels 22-34 and an adjacent pixel is masked and thus non-illuminated, or dark. It will be apparent from FIG. 2 that the illumination intensity of each pixel 22-34 is substantially uniform across the surface of the pixel. Thus, the sole function of the depixellation film used in prior art liquid crystal displays is to "smooth" the abrupt change in intensity between adjacent pixels illuminated at substantially different intensities, such as the pixels 28, 30 of FIG. 2.
The illumination intensity along the line 2--2 for a field-emission display is illustrated in FIG. 3. (Once again, only seven of the hundreds or thousands of pixels along line 2--2 are illustrated.) As illustrated in FIG. 3, seven pixels 42-54 are illuminated at varying intensity. However, unlike the pixel illumination of liquid crystal displays illustrated in FIG. 2, the field-emission display pixels are not uniformly illuminated across the surface of the pixel. Instead, the intensity peaks toward the center of each pixel 42-54. Furthermore, the location of the peak intensity, as well as the manner in which the intensity decreases toward the edges, can vary from one pixel to the next. Significantly, however, the abrupt changes in illumination intensity from one pixel to the next is not present in the illumination characteristics of field-emission displays, as illustrated in FIG. 3. Thus, there is no apparent need for using the depixellation films commonly used with liquid crystal displays. However, the non-uniformity of illumination within the pixels degrades the appearance of field emission displays in manners that do not occur in liquid crystal displays since the illumination within the pixels is uniform. There has heretofore been no solution to the degradation in viewing characteristics of field-emission displays resulting from this non-uniformity of pixel illumination.